Process of treating steel and steel alloys.



bran STATES PATENT curios.

WILLIAM H. JONES, 0h" MU'NHALL, AND ANDREW F. MITCHELL, OF HOMESTEAD,PENNSYLVANIA.

PROCESS OF TREATING STEEL AND STEEL ALLGYS.

ove ace.

No Drawing.

Patented Oct. 28, 1913.

To all 107mm it may concern:

Be it known that we, WILLIAM H. J ONES, of Munhall, and ANDREW h.MITcnELL, of Homestead, in the county of Allegheny and State ofPennsylvania, have invented certain new and useful Improvements inProcesses of Treating Steel and Steel Alloys, of which the following isa full, clear, and eX- act description.

Our invention relates to the treatment of steel and steel alloys whichhave been shaped or partly shaped from the ingot into which the moltenmetal is cast and the invention is designed to provide an improvedmethod of treating the steel whereby its structure is changed and thestrength and toughness of the hardened steel are increased.

One method heretofore used for treating steel to increase its hardnessand toughness is to super-carburizepart or the whole of the perimetricsurface of the steel and then harden by heating and water quenching thesteel. When such super-carburized steel is afterward hardened thesuper-carburized portion of the steel has a coarse crystalline structureso extremely brittle that the outer surface is easily cracked and liableto flake off or spawl when subjected to the uses for which the steel isintended.

One object of our invention is to provide a novel method of treatingsteel such as is used in making rolls for rolling mills, die blocks,rolls used in cold rolling other steel, race rings for roller and ballbearings, and steel articles generally requiring an extremely hard outeror wearing surface formed integral with a relatively soft tougherinterior or back, and the disadvantages above described thereby avoidedand overcome.

in the practice of our improved method, steel or a steel alloy of thedesired composition is first super-carburized by any of the variousWell-known super-carburizing methods. By means of this operation, steelcontaining, say .30 per cent. carbon is superearburized so as to obtainabout 1.5 per cent. of carbon on the outer surface or the desired partof such outer surface of the steel. This super-carburization extendsinwardly from a maximum amount at the outer surface to a depth of aboutone and one half inches, more or less, from the surface, the amount ofcarbon present gradually decreasing in Wardly until the original carboncontent of the steel before recarburizing is'reached. In the second ordecarburizing step of our improved method, such super-carburized steelis then decarburized on its outer surface, the depth to which thedecarburizing operation extends varying according to the decarburisingagent used and the length of time the decarburizing operation iscontinued. The steel, which preferably has been super-carburized on thedesired portions of its outer surface in accordance witlrthe above described method, is decarburized by placing the steel within a box ofsuitable refractory material with the surface or surfaces to bedecarburized adjacent to or resting upon a bed of silica sand or finelyground iron ore, and is heated to a temperature approximating 1025degrees centigrade for a varying length of time (from two to eight days)dcpending upon the depth to which the doomburizing is to be effected. inthis operation, the surface of the metal will be decarburized to thepoint where it is practically free from or very low in carbon and inaccordance with our method the steel may originally be made of suchthickness or diameter as to allow this outer surface to be removed bymachining, after the decarburizing opera tion is completed. In this waythe very soft decarburized surface will be removed and the new surfacethus obtained will have a carbon content of from. .00 to .80 per cent,this amount of carbon being sufficient to afford a hard wearing surfaceafter being later subjected to the hardening operation.

Another Way of providing the desired carbon content of from .60 to .80per cent. at the surface of the steel after decarburiaing, is to againinclose the steel within a covering of suitable refractory material,after covering the decarburized surface with a mild recarburizing agent,and then heat the steel to a temperature of about 975 degrees centigradefor a period of from about 1.0 to as high as 24 hours, in this wayrecarburizing or again increasing the carbon content of the outersurface to the desired extent.

After the decarburized portions of the supercarburized steel have beentreated,

either by machining to remove the outer decarburized surface, or byrecarburizlng to increase the carbon content of the decarburizedsurface, the steel is then tempered or hardened by heating and quenchingin Water, oil or other cooling medium in the usual manner, thisoperation providing the outer surface of the steel with a very hardWearing surface of fine, clear chill structure similar to that of toolsteel, which is joined to the soft tough portion of interior having afibrous structure. In some cases the steel may be heated and quenched inwater in or der to harden after the completion of the decarburization ofthe sutm'earbur-ized face and'the step of removing part of thedecarburized face portion omitted. In this a steel having two distinctlayersor strata is provided in which the outer surface is of glasshardness and has a fine clear chill and the second layer or stratumhaving a corn-f paratively soft fibrous structure which is tough andvery strong. v H e The advantages of our invention will be apparent tothose skilled in the art. our improved method of treating the steel theadvantages of the very hard super -carbuf rized steel are retained,while the wearing e (in treating steel having a fibrous portion surfaceof the steel is changed 'trom coarsely crystalline structure to a fineclear chill structure of the nature of tool steel which permits oftempering to the required degree of hardness; while increasing thestrength and wearing qualities of this outer surface and providing asurface which will 1 not readily spawl off or crack when inuse: The softfibrous layer of steel affords great strength and in this way a hardeneds'uper- 1 carburized' steel not" heretofore known is provided; 7

I Modificatlons may be made 1 n thema'nner of carrying out the stepscomprising out im proved method Without departing from our 1 invention.7

lve'eclaim 1. The method of treating supercarburized steel consisting indecarburizing for a portion of the depth of supercarburization, removinga portion of the decarburized surfaceof the steel and then hardening thesotreated steel;

2. The method of treating steel having a supercarburized face portion,consisting in decarburiiing said face portion, removing part of thedecarburl'zed face portlon by machining and then hardening the sotreatedsteeh I V v k 3; The method of treating supercarburized steel consistingin. decarburizing for aportion' of the depth of supercarburization,removinga portlon of the decarburized surface of the steel by machiningand then hardening the so-treated steel.

4 The method of treating steel consisting j'oin ed integrallyto asupercarburized face port-ion by decarburizmg the supercarburized facefor a portion of the depth thereof, removing the decarburized faceportion by machiningand then water hardening.

wit,ness* whereof, We have hereunto set our hands. e e V WVILLIAM H.JONES. ANDREW F. MITCHELL.

\Vitnesses ARTHUR PARKER, E. H. TEwKsB'U'RY.

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